According to the prior art, during cold grinding, a product to be comminuted, in particular plastic, is embrittled by cooling with a coolant and is fed to a mill for comminution. The comminuted product leaves the mill in a cold state, is collected and stored temporarily, during which time the temperature of the ground product adapts to the ambient temperature. During this storage, electrostatic charging which has formed on the ground product can die away. In order to improve the subsequent sifting of the ground product, in many cases a separating agent is added. The latter is admixed with the ground product. During sifting, the oversize grain is separated from the fines and can be fed to the grinding process again. While the temperature of the ground product adapts to the ambient temperature during the temporary storage, water from the ambient air condenses on the particles of the ground product. As a result, the siftability of the ground product is severely restricted. Intermediate drying and adding separating agents therefore cannot be dispensed with for sifting in the previous cold grinding process. The operating stages involved with this are time-consuming and costly.
For instance, the production of fines has to be interrupted for the duration of temporary storage, and costs are incurred for the use of the separating agent and the work this involves.
German Patent Specification 38 33 830 C2 shows an apparatus of the applicant for the manufacture of extremely fine dusts with particle sizes up to less than 10 micrometers, which includes a sifter. EP 0,044,507 A1 describes a process in which labels are separated from plastic items by sifting. EP 0,317,935 B1 illustrates an apparatus in which the cold gas emerging from a mill is freed from particles by means of a cyclone. In German Offenlegungsschrift 23 18 549, the product comminuted by cold grinding is sized by means of a screening device. The publications cited in the prior art relate either to the manufacture of extremely fine dusts or they are based on different objects. For instance, in EP 0,044,507 A1, separation takes place not by particle size, but by material property.